Silicon carbanion chemistry

THE SYNTHESIS OF SILICON CONTAINING POLYMERS VIA CARBANION CHEMISTRY... 

In some of the syntheses described above, carbanion or carbanion-like intermediates are used to make silicon containing monomers or polymers. Our group has done extensive work in carbanion chemistry for monomer and polymer synthesis. This work describes the use of two dicarbanion species in the preparation of several different silicon containing monomers and polymers. Some of this work closely parallels the work described above in that similar reaction schemes are utilized, but the final polymers are all different (except one). The goal of this research was to prepare different types of dicarbanions and place those moieties in a polymer backbone via Si bonds. By selecting silicon-carbon bonds and/or siloxane bonds, we were able to substantially vary the properties of the final polymers. 

In contrast to the transition metals, where there is often a change in oxidation level at the metal during the reaction, there is usually no change in oxidation level for boron, silicon, and tin compounds. The synthetically important reactions of these three groups of compounds involve transfer of a carbon substituent with one (radical equivalent) or two (carbanion equivalent) electrons to a reactive carbon center. Here we focus on the nonradical reactions and deal with radical reactions in Chapter 10. We have already introduced one important aspect of boron and tin chemistry in the transmetallation reactions involved in Pd-catalyzed cross-coupling reactions, discussed... 

Many reactions encountered in organosilicon chemistry involve the formation of carbocations on a carbon atom (3 to a silicon atom (Si-C-C+) and carbanions on a carbon atom a to a silicon atom (Si-C"). 

Publications which cover wide areas of organophosphorus chemistry have appeared. These include a whole edition of Chemical Reviews (1994, 94, issue 5) devoted to Organophosphorus Chemistry and the Proceedings of the XU International Conference on Phosphorus Chemistry (ICPC XII - Toulouse, 1992) which have been published in Phosphorus Sulfur and Silicon (1993, volumes 75, 76, and 77). Both of these contain much of interest and illustrate the current importance of the subject. ICPC XIII takes place this year (1995) in Jerusalem and we will report on this in volume 27. A new edition of Johnson s excellent book Ylides and Imines of Phosphorus has been published almost thirty years after the original and is indispensable to anyone who studies or uses ylides, phosphorus-stabilised carbanions or imines. 

Silicon.— Allylsilanes are outstandingly useful carbon nucleophiles as a result of their ability to react with electrophiles in a controlled and specific manner to form new carbon-carbon bonds. Furthermore, metallation to give a-(trimethyl-silyl)allylic carbanions introduces the possibility of an additional level of control over the mode of attack (either a or y) exhibited by the allylsilane. It is not surprising, therefore, to find the chemistry of these species occupying a prominent position in this year s organosilicon literature, and in addition to the many applications reported some new routes to these compounds have been described. One such example is shown in Scheme 13, in which the starting silyl sulphone is readily prepared by oxidation of the product obtained from reaction of thio-phenol with vinyltrimethylsilane." ... 

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